The present invention relates to an analog/digital converter and a millimeter wave radar system, and relates, for example, to a calibration technique in a MASH (Multi stAge Noise SHaping) type or sigma-delta (ΣΔ) type analog/digital converter.
For example, U.S. Pat. No. 6,970,120 discloses an analog/digital converter circuit including a calibration circuit which searches for a filter coefficient of a calibration filter. The calibration circuit inputs a pseudo-random signal to the analog/digital converter circuit, in a start-up time of the analog/digital converter circuit, and searches for a filter coefficient while observing the final output.
Non-Patent Literature 1 (Yun-Shiang Shu and four others, “LMS-Based Noise Leakage Calibration of Cascaded Continuous-Time A Modulators”, IEEE JSSC, Vol.45, February 2010, p.368-379) discloses a method for performing calibration in a manner that a time constant of an analog loop filter coincides with that of a digital noise cancel filter, in ΔΣ modulator. Particularly, the time constant of the analog loop filter is searched using an LMS (Leas Mean Square) algorithm, while injecting binary pulses to a quantizer. This analog loop filter is to zeroize residual power in the final output.